A double-to-string conversion algorithm based on Schubfach

• Round trip guarantee
• Shortest decimal representation
• Correct rounding
• High performance
• Fast compile time
• Zero dependencies
• Small, clean codebase consisting of one source file and one header
• Permissive license

#include "zmij.h"
#include <stdio.h>

int main() {
  char buf[zmij::buffer_size];
  zmij::dtoa(6.62607015e-34, buf);
  puts(buf);
}

More than 3x faster than Ryu used by multiple C++ standard library implementations and ~2x faster than Schubfach on dtoa-benchmark run on Apple M1.

Compile time is ~60ms by default and ~68ms with optimizations enabled as measured by

% time c++ -c -std=c++20 schubfach.cc [-O2]

taking the best of 3 runs.

• Selection from 1-3 candidates instead of 2-4
• Fewer integer multiplications in the shorter case
• Faster logarithm approximations
• Faster division and modulo
• Fewer conditional branches
• More efficient significand and exponent output